Extraction of lignosulphonic acid



J y 39430 W. c. PRITCHARD ET AL 3 5 EXTRACTION 0F LIGNO'SULPHONIC ACID Original Filed Aug. 8, 1938 WAsTE SULHTE LIQUOR (CoNcENTRATE 0) DILUTION BY ADDITION OF EQUWALENT-QUANTITY OF H 0 Fl LT RATE Dnscnnoeo F1 LTRATE Qmmms Sueassfiqnums PRECIPITATE QqaouYDRA-rEs E'rc. L

LIGNO Suuomc ACID/4ND Q150 WASH WIT 1.3 H 50 FILTIiATE P FILTRATE RECIIITATE DECARDED Mzx WITH H O To DISSOLVE Lucma fiuLFomc A010 Preecugrm-rs DISCARD PRECIPITATE Cou'rnmme CA5O4 F'LTRATE LIGNO 5uu=omc Acm i I ALTERNATIVE PURIFIICATION TREATMENT TREAT Wane CACO To PRECWTATE PREGIPETATE Exczss H 50 lA/J/Ibm QFn'zfc/rard DISCARD CR 5 0 Am: Haber! HUaz /y Excess c1400 F'LTRATE x B Lac-mo fiuuFomo A010 j Patented July 27, 1943 EXTRACTION OF LIGNOSULPHONIC ACID William 0. Pritchard-and Robert A. Daily, Muscic. Ind., assiznors to General Motors Corporation, Detroit,

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lllicln, a corporation or Dela- Original application August 3, 1938, Serial No. 223,706. Divided and this application January 25, 1940, Serial No. 315,470

2 Claims. (Cl. 260- 124) This application is a division of Ser. No. 223,706 filed August 8, 1938 Patent No. 2,217,814, October 15, 1940. g

This invention relates to a method of extracting substantially pure iigno-sulphonic acid from waste sulphite liquor.

An object of the invention is to provide a method whereby certain desirable constituents, such as ligno-sulphonic acid, in waste sulphite liquor may be readily extracted therefrom for subsequent use as an addition agent in the negative paste of storage battery plates, for giving the plates increased life and capacity, particularly at low ambient temperatures.

It is a further object of the invention to provide a method whereby the ligno-sulphonic acid may be inexpensively extracted in the substantially pure state from waste sulphite liquor.

Further objects and advantages of the present invention will be apparent from the following calcium bisulphite and sulphurous acid. Thecomposition of waste sulphite liquor is extremely complex in nature deriving its constituents from practically all ingredients that are originally present in wood, with the exception of cellulose which is separated by filtration after the digestion of the wood in aforementioned solution. During this digestion step the sulphurous acid chemically acts upon the insoluble lignins, sugars, tannins,

- resins and carbohydrates to cause the same to go into solution. The combination of the calcium 'bi-sulphite and sulphurous acid also produce some organic calcium compounds.

In application Serial No. 173,863, assigned to the assignees of the present application, the use of ligno-sulphonic acid is disclosed together with one method of separating said acid in a substantially pure state from waste sulphite liquor. Our invention as contained herein is particularly -directed to another method, whereby ligno-sulphouic acid in the substantially pure state can be readily and inexpensively extracted from the complex waste liquor. We have found that ligno-sulphonic acid is the only desirable constituent in waste sulphite' liquor for use as an addition agent in storage battery paste. We have further found that the remaining compounds in the waste sulphite liquor and particularly the calcium compounds are not only unnecessary in this addition agent, but are undesirable, since they decrease the porosity of the paste and of the final active material. Stated differently, the active material formed, by using waste sulphite liquor as the addition agent thereto is more dense and therefore more costly, since a greater quanty of oxide of lead is necessary in the manufacture of the plates. Ligno-sulphonic acid in the substantially pure state prepared according to the hereindescribed method is an ideal addition agent ior battery paste since the addition of the ligno-sulphonic acid does not decrease the porosity of the active material of the plate and hence does not'increase the plate weight. The waste sulphite liquor of commerce is available on the market in a sirupy form containing about 50% water and about 50% solid. This condition is brought about by neutralization of the liquor, as it comes from the digestors, with either lime or magnesia to remove the excess sulphurous acid, filtering out this insoluble precipitate and evaporating the filtrate to the desired consistency. In accordance with our invention, waste sulphite liquor of commerce is diluted with an equivalent quantity of water to produce a resultant solution containing about 25% total solids. Sulphuric acid having a specific gravity of about 1.400 is then added to the solution in suflicient quantity to bring the specific gravity of the mixture to about 1.300. Sulphuric acid reacts with calcium salts in waste sulphite liquor to form a precipitate of calcium sulphate and set w the ligno-sulphonic acid free in the precipitated form, as well as precipitate any free ligno-sulphonic acid that is in solution. Lignosulphonic acid is insoluble in sulphuric acid solutions having a specific gravity approximating the gravity of the solution present. The compounds containing the sugars, tannins, carbohydrates, etc., remain in the solution in the dissolved state. The next step in the process is to filter out the precipitate containing the ligno-sulphonic acid and the calcium sulphate and wash the same with a sulphuric acid solution of approximately 1.300 specific gravity, which has no tendency to dissolve the ligno-sulphonic acid, the filtrate in both instances being discarded.

The washed precipitate is next mixed with water, which dissolves out the ligno-sulphonic acid and leaves calcium sulphate as an insoluble residue. This solution is then filtered and the residue of calcium sulphate is then discarded. Th filtrate which consists of ligno-sulphonic acid, water and a small amount of entrapped sulphuric acid may then be treated with an excess of calcium carbonate which reacts with the sulphuric acidto precipitate out as calcium sulphate. This solution is then filtered to remove the excess carbonate and the precipitated calcium sulphate.

The step of purifying the filtrate by removing carbonate may be omitted ifdesired, since sulphuric acid is used in the preparation of the paste mixture and the amount introduced in conjunction with the ligno-sulphonic acid is negligible.

The quantity of ligno-sulphonic acid solution to be used in the paste mixture varies-in accordance oi the concentration of the ligno-sulphonic acid therein. We have found that optimum conditions are obtained when using ligno-sulphonic acid in percentages from .05% to .1% based on the weight of the paste. It is our belief that this small percentage of ligno-sulphonic acid acts in efl'ect as an addition agent rather than as an expander in the-common use of the word. It prevents crystal growth of the lead particles of the negative plate at the beginning of formation and throughout the life of the plate. As far as we can determine there is no swelling or expanding of the ligno-sulphonic acid itself.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form,

the free sulphuric acid by the addition of calcium it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A' process for extracting ligno-sulphonic acid in the substantially pure state from waste sulphite liquor for use as an addition agent in storage battery paste comprising, treating the waste sulphite liquor with sulphuric acid to bring the specific gravity of the solution to 1.3 and to form a precipitate containing ligno-sulphonic acid, which is separated from the remainder of the liquor and then dissolving out the ligno-sulphonic acid from the precipitate by the action of water, and thereby separating the ligno-sulphonic acid from the insoluble matter.

2. A process for extracting substantially pure ligno-sulphonic acid from waste sulphite liquor comprising the steps of, precipitating ligno-sulphonic acid and calcium sulphate from waste sulphite liquor by the addition of sufllcient sulphuric acid to bring the specific gravity of the solution to 1.3, and separating the precipitate from the remainder of the sulphite liquor, dissolving out ligno-sulphonic acid from said precipitate by the ligno sulphonic acid.

WILLIAM C.PR.ITCl-1ARD. ROBERT A. DAILY. 

